There is a great appearance that, immediately after the mixture of the two seminal liquors, the whole materials of generation exist in the matrix under the form of a globe; since we know, by anatomists, that three or four days after conception there is a small oval ball in the matrix, this ball is formed by an extremely fine membrane, which incloses a limpid liquor like the white of an egg. We can then perceive some small united fibres in this liquor, which are the first outlines of the fœtus. A net-work of fine fibres collects on the surface of the ball, which extends from one of the extremities to the middle. These are the first vestiges of the placenta.
Seven days after conception we may distinguish, by the naked eye, the first lineaments of the fœtus, as yet unformed; being only a mass of transparent jelly, which has acquired some small degree of solidity; the head and trunk are easily discernible, because this mass is of an oblong form, and the trunk is more delicate and somewhat longer. Some small fibres, in form of a plume of feathers, spring from the body of the fœtus, and which turn towards the membrane in which it is included; these fibres are to form the umbilical cord.
Fifteen days after conception, the head, and the most apparent features of the face, are distinguishable; the nose resembles a small prominent and perpendicular thread affixed to a line, which indicates the division of the lips. Two small black points are in the places of the eyes, and two little holes in those of the ears; the body of the fœtus has also received some growth. On each side of the upper and inferior parts of the trunk, little protuberances appear, which are the first outlines of the arms and legs.
Eight days after, that is in three weeks, the body of the fœtus has only increased about a line; but the arms and legs, the hands and feet, are apparent; the growth of the arms is more quick than that of the legs, and the fingers separate sooner than the toes. At this time internal organization begins to be discernible; the bones appear like small threads as fine as hairs; the ribs are disposed regularly from the two sides of the back bone; and as well as the arms, legs, fingers, and toes, are represented by very small threads.
At a month the fœtus is more than an inch long; it naturally takes a curved posture, in the middle of the liquor which surrounds it, and the membranes which contain the whole are increased in extent and thickness; the mass is oval, and it is then about an inch and an half in its greatest, and an inch and a quarter the smallest diameter. The human figure is no longer equivocal, every part of the face is already discernible; the body is fashioned, the thighs and belly are seen, the limbs formed, the toes and fingers divided, the skin thin and transparent, the viscera marked by fibres, the vessels as fine as threads, and the membranes extremely delicate, the bones are as yet soft, and have only taken solidity in some few parts; the vessels which compose the umbilical cord, are as yet in a straight line by the side of each other; now the placenta only occupies a third of the whole mass; whereas in the beginning it occupied the half. It appears, therefore, that its growth, in superficial extent, has not been so great as that of the fœtus, and the rest of the mass; but it has increased much more in solidity; its thickness has become greater in proportion than the membranes of the fœtus, both of which are now easily distinguished.
According to Hippocrates, the male fœtus is developed sooner than the female. He says all parts of the body in the first are apparent in thirty, whereas the latter are not so till the expiration of forty-two days.
In six weeks the fœtus is nearly two inches long; the human figure begins to be more perfect; the head is only larger in proportion than the other parts of the body; the motion of the heart is perceived about this time. It has been seen to beat in a fœtus of sixty days, a long while after it had been taken out of the womb of its mother.
In two months the fœtus is more than two inches long; the ossification is discernible as far as the middle of the arm, thigh, and leg, and in the point of the lower jaw, which is then very forward before the upper. These, however, are only ossified points; but by the effect of a more ready expansion, the clavicles are wholly ossified. The umbilical cord is formed, and the vessels which compose it, begin to twist nearly like threads which compose a rope: but this cord is still very short in comparison of what it becomes hereafter.
In three months the fœtus is nearly three inches long, and weighs about three ounces. Hippocrates says, that it is at this time the motion of the male fœtus begins to be felt by its mother; but that those of the female are not felt till after the fourth; there are women who affirm they have felt the motions of the child at the beginning of the second month. It is very difficult to be certain on this subject, the sensations excited by the first motions of the fœtus depending, perhaps more on the sensibility of the mother than the strength of the child.